I got a mossberg 835 and I'm wanting a red dot on it for turkey season but I'm not sure what one would be good with the 31/2 inch shells I'm goin to be using and I'm on a small budget 100 buck or less thanks for for your help

Use that money to buy shells and practice. That will help more thasn a dot.

Aiming ain't the problem my eyes suck and I can't see my bead clear enuff I had a fiber optic sight on it but recoil knock it off and I couldn't find it the other day when I was shooting some 31/2 00buck so the why I'm thinking about a red dot maybe a fix power scope

Bushnell, TRS 25 has worked well on my AR and Marlin .30-30. Old Tasco Propoints that were made in Japan before operations were moved to China, are pretty tough, and you can find them on E-Bay from time to time. I had a PDP2 that went for years with no trouble at all. Finally had a friend talk me out of it for his kid's AR. Still running on that rifle.